Induction-furnace lining



Aug. 9, 1932. N. R. DAVIS ET AL INDUCTION FURNACE LI'NING Filed May 14, 1930 INVENTORS, Nev/lie 1e Dav/ls and 6$arge 17. Wood.

AT'TORNEY 4 Patented Aug. 9, 1932 UNITED STATES-PATENT} oFF cE NEVILLE RYLAIND DAVIE, OI ASET'OIN-GIT-KERSIEY, AND GEORGE .ANDREW WOOD, OF

I WESTINGHOUSE ELECTRIC AND MANUFAG- I TUBING 001mm, A COBPOEA'IION OF PENNSYLVANIA snarrrmn, ENGLAND, nssrouoas 'ro mnuc'rIoN-rummcn Lmme Application filed Hay, 1880, Serial No.

Our invention relates to furnacesand more particularly to electric induction furnaces.

An object of our invention is to provide a hi hly eihcient and highly resistant lining of re mctory material for an electric induction furnace. 7

Another object of our invention is to pro vide a refractory linin which shall embody material giving it di erent degrees of refractoriness longitudinally of the melting chamber.

In practicing our; invention, we provide a refractory lining which may .includamagnesite, with lime as a bonding material, to which is added varying percentages of a mineralizer, such as borax, iron oxide or glass.

The amount of added material is relatively small at that part of the lining subjected to the largest amount of wear and decreases toward'the top of the furnace to provide "a lining of higher refractoriness at the lower portions of the chamber.

The single figure of the drawing is aview, in vertical section, of a coreless induction furnace embodying our invention. 1

The linings or crucibles of electric induction furnaces are usually prepared by locating a tubular template within an outer peripheral metal casing, between which is located a heating coil. The space between the template and the casing and around the coil is filled by an initially granular, refractory material which is rammed into place and 15 then sintered, as b heating the template by energizing the coi or by melting a charge therein. If the refractory lining is of substantially the same degree of refractoriness from top to bottom, it has been found that the upper portions of the linings are insufficiently sintered and,-therefore, have a tendenoy to crumble, this being particularly noticeable at the upper edge or rim of the lining which is, of course, usually located Well above the upper turns of the energizing coil.

Referring to the drawing, we have illustrated a casing 11, which may be of metal, an energizing coil 12 therein and a lining .13 of granular electric-insulating refractory no material, the composition of which more par- 452,206; and in Great Britain Kay 15, 192a tubular shape, is located in the casing 11, to

cooperate therewith in initially holding the fining during the assembly of the furnace and to define a furnace chamber 16. A cover 17, having a pouring spout 18, may be provided. We have illustrated a specific embodiment of furnace structure in order to illustrate the use of our invention therewith, and desire it to be understood that the details of the casing, heating coil-template and cover are not parts of our invention. The normal material of the lining 13 may consist of a major portion of magnesite, say on the order of per cent, to which is added a self-hardening bonding material, such as (lime; In order to obtain a gradation of the degree of refractoriness, we may add such materials as glass, iron oxide, or borax.

We may add about 6% or 7% of borax to the material which is located at the botof the furnace lining and, at a point' some 6 inches or so from the bottom, where the erosion in a coreless induction furnace is likely to bethe most rapid, indicated by /the line marked 19 the lining materi' i may be made more refractory by the addi ion of a lesser percentage of borax, say on th order of 4%. The percentage of borax may he increased above this' oint until it reaches about 15%" at What may called the wash line of thecharge, indicated by the line 21. The percefitfi'ge of borax may be on the orde of 25% around the timer top of the lining, at the line 22, and we may add about 5% of dextrine to constitute a bond. d

When a lining of this kind is treated in the ordinary manner, after having been tightly rammed into place, by heating a normal charge ormetal template therein, the maximum temperature'is developed in the zone indicated by the line 19 at which the lining is most refractory, and, as a result, this lining is adequately sintered at this zone. Since the zones indicated by the lines 21 and 22 at which the temperature'developed is lower are composed of less refractory or more easily sintered materiahthese zones are also adequately sintered, and the surface of the linin subjected in the ordinary operation of the furnace. We believe that the action ofthe borax or similar material added to the magnesite and lime, is substantially as follows: The borax constitutes an additional flux for the magnesite at the lower range of temperature and then acts as a flux at intermediate temperatures. It vaporizes at the higher temperatures, and the fluxed ma esite is probably recrystallized so that it is of greater refractoriness than before. It may thus be said that the borax acts as a mineralizer for the granular refractory material.

The varying percentages of borax is in accordance with the degree of sintering which is effected by the coil; that is, the degree of refractoriness and of sintering is a maximum near the bottom of the chamber and decreases toward the top, as has been set forth.

Various modifications may be made in the device embodying our invention without departing from the s irit andscope thereof, and we desire, there ore, that only such limitations shall be placed thereon as are imposed by the rior art or are set forth in the appended c aims. I Y

We claim:

1. In an induction furnace, a lining of refractory material defining a materiaLcontaining chamber, said lining bein most refractory at a level slightly above t 0 bottom of the chamber and decreasing in degree of refractoriness with the approach to the topof said chamber.

2. An electric induction furnace including I a lining defining a furnace chamber, said lining comprising a granular refractory ma terial and a relatively small quantity of a material which constitutes a bond at low temperature and a flux at an intermediate tem perature and which vaporizes at higher temperatures to increase the refractoriness of the refractory material, the amount of the second mentioned material increasing from the bottom to the top of the linin 3. An electric induction furnace iaving a lining defining a material-containing chamber, said lining including a major portion rammed and sintered lining defining a material-containing chamber, said lining including a major portion of a granular refractory material and a minor portion of material having the characteristics of borax as a min eralizer, the amount of said last named ma-. terial in said linin varying'longitu'dinally of said chamber an being a maximum at the top thereof.

5. electric furnace having a rammed and sintered lining definin a material-containing chamber, said lining including a major portion of a granular refractory ma terial and a minor portion ofborax to mineralize the ranular refractory material, the amount ofrax increasing toward the top of the lining.

In testimony whereof, we have hereunto subscribed our names this twenty-third day of April, 1930, and this twenty-eighth day of April, 1930.

NEVILLE RYLAND DAVIS. GEORGE ANDREW WOOD.

of a granular refractory material, a minor portion of a self-hardening bonding material and a varying but lesser quantity of a ma terial which constitutes a bond for the granular refractory material at lower temperatures and a flux at intermediate temperature and which vaporizes at higher temperatures to increa'sethe refractoriness of the granular refractory material, the amount of said last named material increasing toward the top of the lining.

4. An electric induction furnace having a y no 

